Method of making chromium containing alloys



Feb. 1o, 1925. 1,525,518

W. H. SMITH ET AL METHOD OF MAKING CHROMIUM CONTAINING ALLOYS FiledSept. l1, 1922 INVENT'oRs. Wmam \"\.5TT\'\Th BY Shades M.Cumpbe\\ ATTORNE Y.

Patented Feb. 10, 1925.

Aum'nezo 'STATES PATENT oFFlcE.

WILLIAM H. SMITH, OF CLEVELAND, AND CHARLES M. CAMPBELL, OF EAST CLEVE-LAND, OHIO, ASSIGNORS TO PIONEER ALLOY PRODUCTS COMPANY, OF CLEVE- LAND,OIHIO., A CORPORATION OF DELAWARE.

METHOD OF MAKING CHROMIUM CONTAINING ALLOYS.

' Application filed September 11, 1922. Serial No. 587,300.

To all whom it may concern: j

Be it known that we, WILLIAM H. SMITH' and CHARLES M. CAMPBELL, citizensof the United States, residing, respectively, at Cleveland and EastCleveland, in the county of Cuyahoga and State of Ohio, have inventedcertain new and useful Improvements in Methods of Making ChromiumContaining Alloys, of which the following is 'a specification, referencebeing had to the accompanying drawing.

Y This invention relates to a method of producing a non-corrodible alloycontaining only elements of low and intricate valu/e, which alloy shallbe suiiiciently soft and tractable to en'able it to "be turned, cut,threaded and otherwise machined. It has long been known that certainalloys of chromium with iron group metals offer a very high degree ofresistance to corrosion, whether at ordin'ary atmospheric temperaturesby water and ordinary gases, or atl high temperatures as in furnaces'andthe like, or on contact with chemical reagents; but diiiiculty hasalwaysbeen experienced in the' preparation of these alloys due to theirpropensity to absorb carbon, silicon and other injurious elements whichserve to increase their hardness to a point which precludes mechanicalfabrication and increasing the brittle-ness to a point which frequentlycauses them to break uponv cooling or lapse of time. Numerous prophesieshave been made thatif an alloy of chromium and Airon could be producedexcluding the carbon, silicon, and other injurious ingredients, the samewould be very soft, uniform, and easy to machine, and such alloys, whenproduced in small quantities under strict laborator methods with pureingredients, have con rmed the prophesy, but it has hithertobeen'impossible to Irepeat the demonstration under production conditionsbecause ofl the avidity of chromium and its alloys for carbon which athigh temperature causes it to decompose even carbon monoxide, and toabsorb carbon `from the electric arc; While l(its avidity for silicon issuch as to cause it to decompose silica either inside the furnace or inthe mold wherein the same is cast. Both these diiiiculties are enhancedby the high melting temperature of the alloy,l which requires longcontinued heating for complete fusion, and at these high "rise to areaction accompanied by bubbling and frothing which frequently causesthe mixture to spout out of the mold, and almost ilways leaves thecastings porous and worthess.

In `our former application filed August 22, 1921, Serial No.494,055 wedescribed and claimed 'a method vof producing these alloys in anelectric'furnace ofthe arc type wherein the molten bath is alwaysshielded from the arc by the interposition of an unbroken slag layerwhich is electrically conductive at the high temperature involved. Wehave discovered, however, that while it is possible to secure small andsimple castings directly by this process, it is not feasible to securelarger and intricate castings in this way, since if the temperature beforced sufficiently high to produce a degree of fluidity of the moltenbath necessary for the production of such a casting, the are will almostcertainly puncturethe slag and so contaminate the bath as a result ofdissolved carbon that the casting will be hard to machines Furthermorethe constant lvariation in temperature required when the same furnace isemployed bothfor melting the alloy and bringing it to the casting pointnecessitates a constant variation in the composition of the slag whichis diilicult -to effect.

way the first furnace can conveniently be" operated within asuiiiciently sm'all range of'temperature to 'enable'the use of a slag ofone composition, and with a minimum of injury to the hearth and walls;while the second furnace merely receives the molten metal atthe-temperature most conveniently maintained in the first furnace andboosts this temperature quickly to the pouring temperature with aminimum current expenditure and minimum alloy contamination. Smallmetallic additions such as tungsten, molybdenum, zirconium, manganese,and the like are 'also preferably added in this second furnace. l

vIn the drawing accompanying and forming a part of this application Wehave shown somewhat diagrammatically the steps of our improved process;Fig. l represents the arc furnace with its charge prior to melting; Fig.2 illustrates the same furnace with its charge molten; and Fig. 3represents an induction furnace with its charge. A

1 represents the hearth of the arc furnace, 2--2 the electrodes, whichare located en` tirely above the surface of the metal bath. The iron isthrown or piled in the center of the hearth as shown at A, the nickel(when used) around it as shown at B, and the ferrochrome around that asshown at C, the last being kept out of contact with the electrodes andcovered with a` mixture of lime and luorspar D, some three or fourinches deep. g

This lime and fluorspar must be of good.y quality, mixed thoroughlytogether in theproportion of about 80% to- 90% of lime and the balancefluorspar. The furnace is thenstarted in the usual manner and as soon asthe iron has melted the heat thereofslowly causes the ferro-chrome todis` solve therein and the slag to soften and flow thereover so that thearc can no longer strike through the slag into contact with the'moltenmass. This is rendered possible by the fact that the slag becomesconducting under the temperature of the electric arc. The preferred slagcontains about 90%y lime and 10% iiuo-rspar.

As soon as the metal has been brought to a condition of uniformcomposition it ,is drawn into the second furnace which is preferably ofthe induction type for the reason that the latter produces its heat enanamount of molten alloy continuously inv the first furnace, each. pourbeing immediately replenished by the necessaryl quantity of iron-andferrochrome, with or without nickel. Onl a short timepand smallexpenditure o current is requiredto elevate the temperature to thepouring degree in the second furnace. The alloy is cast in molds of anysuitable or desired type and material excepting that we prefer to employone which contains no silica.

lVe do not limit ourselves to the described method of char ing thefurnace as we can equally well buIld the iron on top of theferrochrome;neither do we limit ourselves Ato any xed relative sizes between thefurnaces, nor to a process of drawing off only a part of the alloy fromthe firsty preliminary arc furnace, at a comparatively low temperature,beneath an electrically conductmg, carbon-free slag, transferring themolten alloy to an induction furnace andv there' raising it to a pouringtemperature under neutral conditions.

2. The process of producing low-carbon, alloys of chromium withiron-group metals,

which contains the steps of melting the iron group metals in an electricarc furnace in:

direct contact with the arc, adding the l chromium together with acarbon-free elec'- trically conducting slag, transferring the moltenalloy to a second furnace at a temperature only slightly above fusion,and heating the charge in the second furnace to a pouring temperatureout of contact with carbon.

3. The process of producing low-carbon alloys containing chromium andiron-grup metals, which contains the steps of vmelting the essentialingredients in an arc furnace at a comparatively low temperature beneathan electrically conducting carbon-free slag, transferring the same to aninduction furnace, at a temperature only .slightly above fusion, addingfurther ingredients in said induction furnace, elevating theternperature therein to that of casting, and fi-` 4 nally casting fromsaid second furnace.

In testimony whereof, we hereunto affix our Slg-natures.

WILLIAM H. `SMITH. CHARLES M. CAMPBELL.

